Steering gear construction



April 14, 1953 F. B. BURT STEERING GEAR CONSTRUCTION Filed Oct. 26, 1949 IN VEN TOR. ii/Plflll 5. 50/?7 BY M 3 W4 Patented Apr. 14, 1953 UNITED STATES PATENT OFFICE STEERING GEAR CONSTRUCTION Farlow B. Burt, South Bend, Ind., assignor to Bendix Aviation Corporation, South Bend, 1116., a corporation of Delaware Application October 26, 1949, Serial No. 123,627

6 Claims. (Cl. 74-459) This invention relates to steering gear construction and more particularly to screw and nut gears of the type wherein the screw and nut are provided with corresponding helical grooves for receiving balls which constitute force transmitting members between the screw and nut, and in which said balls are preloaded by adjusting said nut axially.

It is an important object of the invention to provide novel means for preloading the balls in a screw and nut construction of the above mentioned design.

Another important object of the'invention resides in the provision of a ballnut and screw construction wherein two axially adjustable nuts are provided for movement in opposite directions to preload the balls, thus minimizing backlash.

A further object of the invention resides in the provision of novel means in a worm and ballnut steering gear for confiningthe balls to a single helical groove of the worm' and nut.

The above and other objects'and features of the invention may be apparent from the following description taken in connection-with the accompanying drawing which forms a part of this specification and in which:

Figure l is a longitudinal sectional view of one form of steering mechanism with which the invention is associated;

Figure 2 is a view in perspective of the Wormand ballnut;

Figure 3 is a view in perspective of the shunt element for redirecting the balls across the worm crest to the adjacent groove;;and

Figure 4 is a modified form of the shunt element.

Referring now to Figure l of the. drawing in which the invention is illustrated in connection with a steering mechanism, the reference numeral l designates a housing or motor cylinder in which a nut member or piston I2 is positioned for axial displacement within the cylinder. The nut member or piston 12 divides the cylinder into, opposed chambers I4 and IS. Axial displacement of the nut member may be accomplished through rotation of a shaft or worm l 8 which extends through the piston and housing and which is drivably connected to the nut member through a plurality of force transmitting members or balls 20. The rotative action of the shaft is translated into an axial force onthe nut to thereby move the piston to the right or left depending upon the direction of rotation of the shaft. This piston movement is augmented by fluid under pressure from a source, not shown, acting in one or the other of chambers l4 and l6, when thereslstance offered to turning the shaft l8 exceeds a predetermined value determined bythe strength'of a. spring 22. The

, spring normally .holds an open center valve 24 in the position shown tofthereby admit fluid pressure simultaneouslyrto the chambers l4 and It through the passages 26 and 28 respectively. Since the effective areas of the ends of the nut member [2 exposed to fluid under pressure are the same there is no movement of the piston at this time when equal pressures are acting on its ends. The valve is furnished with inlet and outlet passages 30 and 32 communicating with the interior of the valve. The deflection of the spring 22, when theresistance offered to steering exceeds a predetermined value, permits a valve spool to move axially relative to body member 35 so thatone of the passages 26 and 28 is restricted to inlet pressure and opened wider to exhaust pressure and the other of the passages is restricted to exhaust pressure and opened wider to inlet pressure. That is, the reaction to the turning 'efiort is taken in the shaft. whereby axial displacement of the valve 24 is accomplished. Since this valve and its function forms no part of the present invention reference is made to Patent No. 1,790,620 for a more detailed discussion of the operation of an open center type valve.

The housing Ill isequipped with end covers an and 42 which support'bushings' 44 and 46,

respectively and in'which'the shaft'l8 rotates. The shaft is provided with a longitudinal bore 48 for equalizing the pressures acting on the ends of the shaft, This longitudinal bore cornmunicates'with the exhaust port 32throu h a radial passage 50 of the shaft and passage 52' in the valve body. A passage 54 in the valve body communicates the right end of the valve body 24 to the exhaust port.

The nut member or piston is drivably connected to a' rockshaft 55 in a manner to be hereinafter described. A rack 58 is carried by the nut member and meshes with a gear sector 60 securely mounted on the rockshaft.

In order to provide a relatively frictionless driving connection between the shaft or screw l8 and the nut member or piston 12, the screw is equipped with a helical groove 62 and the nut member is furnished with ahelical groovefi l corresponding with the helical'groove of the screw to'thereby form a helical channel into which the balls 20 are inserted. In worm and The length of this channel culating the balls.

may be one helix or several helices. In the present disclosure the balls are circulated through a channel approximately one helix in length. The groove 54 is formed in a sleeve or nut 58, 'of which there are two, suitably posi- 5 tioned in the nut member. These sleeve elements in which the grooves 66 are formed, are securely fixed to the nut memberzin za-;mannerhereinafter; described. This construction.;. is conducive to a reduction in the manufacturing cost of the complete assembly. That is, as r against forming the groove 54 in the piston or nut member per se it is much cheaper -to=form this groove in the sleeve or nut,.68.and then se-r curely attach the same to therpiston' sores td= become an integral part thereof. Only one of. the nuts 58 will be described in detail since they are alike structurally. A shunt" l0 joins'=-adjacent grooves in a manner such that the chana nel of balls forms substantially one complete helix aroundthe screw. This shunt is formed in.. the .nut '68 and comprises a slot T01 'passage :12: into=which an integrated .shunt. member .14 is. 111%. sertedfor diverting the balls from one end "of the helixtothe other end.., The shunt member 14 isi::. formed'with a bridge it over whic'hthe balls ride out ofcontact .with the .worm crest when being .7 returned to the adjacent channel: Scoops H18". and 19 are contiguous the ends of the bridg and protrude,intc-.-the grooves of the .screwso as to. actually liftthe balls ontothe bridge. These scoopsare formed ,to face in op-positeidirections, in order .tolift the ballsout of the grooves reardless of the direction ofrrotation of .the screw.

Guiding surfaces .ll'and 8i 'arerlocated at eachfj..

end ,of the bridge above the scoops wand "13 1 respectively, for directing the -balls 1. downwardly. onto the bridge whenrotation .of .fth'e shaft -.is1,in.'.. one directionandfor deflecting-the. balls cifthe bridge into the helical groove -when. rotationrof .4 the shaft is in the'otherdirection. Whenthe. nut is used as shown in Figure 1; that issinserted into a bore 83 of the nut membergorvpiston the latter forms atop for the passage lfij soiasto. confine the balls within theshunt member when. said balls pass from one. end iof the helix .to the. other. However, when. thenut isinot .usedmin. this manner any,suitablecovering over the pas-r sage will suihce, suchfor example,'as acover r75 formed integrally with the shunt..memb.er '14. See Figured for modificatiominwhichi the cover.,.50 is'bent back fofr.insertingtheballs, The rcona struction herein disclosed fonshunting'itheball'sl as aforesaid is'believedfto be noveLandforms a part of this invention.

Inanyscrew and nut construction it is always .155 desirable to .keep backlashltoaminimum. .Witlr, the use of ya ballnutand screw arrangement the 3; most common way for ..reducing,.backlashl .is... too. preload the balls radially. The construction. v.oi.

the mechanism forradial. loading ofthe balls 60..

is more expensive and the number .oiballs inthe ballnut-must be increased beyond that required inthe present invention because afewernumber of the balls are .actuallyhworkingg It is .a rfurther purpose .of .lthis .invention -.to provide. .means for .preloading the ballsnof. the nut memberaxiallyto.thereby reduce backlash. Thetwoinuts 68, ,one of which comes into acntion for .eachndirectionlof. rotationof theshaft l8, are threaded ontosthe screw -13 and .the..n11t. member or. pistonslidithereover sothat. the nuts.- are housed. .in the bore 85. The nuts 58 and bore '83 are provided with axially. milled-slots Blend 8! for receiving a keyj82. The inner .endof/the. bore 83 is formed'witha: reduced section fldin .4 against which one of the nuts 68 abuts. The other nut, which is adjacent the open end of the bore, has its outer end in contact with a collar 86 adjustably supported on the nut member with bolts 88. Tightening these bolts will urge the nut on the right to the left and the nut on the left to the right, thus removing the backlash. Itgrwill be noted thakthernuts "are 'urged or...preloaded in "opposite 'di'rections,-;which means that backlash is entirely eliminated regardless of? the direction of rotation of the screw or shaft l8. Forone direction of rotation of the shaft l8 'the loadis transferred to the rockshaft through one of'- thenuts and for the reverse di- -rectionuof zrotationiof the shaft is the load is transferreditocthearockshaft via the other nut. Preloading theballs axially as hereinbefore explained 'causes 'all'th'e balls disposed in the nuts excepiztthose in the shunt to be urged against the groove in the worm :and the corresponding groove inthe screw so thatthe load is distributed p pl d lly amongst allth'e balls. fr'ompne end of.the..helical .channel:;to..the otherv end; Thatj.v is, each of. the hallsinthe two circuits, exclusive l of those in.the.shunt,.carri.es its share-of the loads.

Although this invention has been described connection with.,.certain specific embodiments the principles are susceptible of numerous other applications .that .willlreadily occur... to persons skilledin the .art...

Having .thus .described the. .various features .of 1 the invention, what I claim as new and. desire to secure by Letters .Patent is;v r

1.. Screw. and nut mechanism. comprising. a: nut. withva helical groove .therein, a;screw'in the,-., nut, witha helical groove 1 corresponding to. thee groove in; the nut and together therewith form-a. ing 1a... helical channel; aplurality ;of balls. insthe channnelsbetween the screw-and;nut.tand=iare ranged side .by side. :soas to substantially,filLthe; channeLa-Dassage. in the nut connectingiadjacent channels of the :helix; .a shuntimember 13f unitary construction; arranged inrthe :passage :to provide an "endless. trackrfor recirculating the balls said shunt memberzincluding"scoops protruding into the grooves of said screw for' redirecting the ballwacross said' 'shunt member :into 'the -=-adjaZ-* centv channel; and a bridge over which" the balls roll in passing between adjacent ch'ann'elsp said scoopsrbeing formed to 'de'fi'ect'th'e balls radial-13?. from the channel for deposit on said bridges 23111 combination; a shaft withan external. helical groove in its surface;-a=nut memberprovided with .a-longitudinal'bore for receiving the shaft? a shoulder formed in "the bore, a pair'of nuts disposed in the bore and having internal" helical igrooves'matingwith the grooves in said shaft= b'all's" engageable' in the grooves of said shaft and nuts, aring "element located 'atfone end of the nut memben'said nuts being located in the: bore between said "shoulder and ring "element, and means associated with the ring 'ele- I ment for urging' said shoulder against one 'end I of one-of said-nuts and'for urging said ring element against the opposite end of the other of" said: nuts; whereby said nuts are -preloaded in opposite direct-ions;

3.-'Incombination, ash'aft'with an external helical groove in its surface, a nut memberpro vided with a-=longitudinal bore for receivingthe' v shaft; a' shoulder fo'rmedin-the bore; a pair-of nuts disposed end to'en'dinithe bore and.hav-. ingqinternal helical grooves, mating with the: grooves in said shaft, ballsv engageable .inthe.

grooves iof .i'said ishaft and. nuts, alring ele'mentlocated at one end of the nut member, said nuts being located in the bore between said shoulder and ring element, axially extending splines in the nut member and nuts, keys in the splines for preventing relative rotation between the nut member and nuts but permitting relative axial movement therebetween, and means associated with the ring element for urging said shoulder against one end of one of said nuts and for urging said ring element against the opposite end of the other nut.

4. A non-friction screw and nut assembly comprising, in combination, a shaft with an external groove in its surface, a pair of nuts, each provided with internal grooves mating with the grooves in the shaft, balls engageable in the grooves of the shaft and nuts, a member arranged concentrically of said shaft to be moved therealong and provided with an opening for receiving said two nuts, an abutment in the opening against which one end of one of the nuts rests, the other nut having one of its ends disposed adjacent the other end of said one nut, an adjustable abutment arranged with respect to the opening to engage the other end of said other nut, and means carried by said member for urging said first mentioned abutment against one end of said one nut and for urging said second mentioned abutment against said other end of said other nut so as to preload said balls.

5. In a screw and nut assembly, a screw having threads thereon, a nut having threads therein for mating with the threads of the screw, a plurality of balls in the mating threads of the screw and nut, said nut having an opening in its wall to provide a passage for connecting two threads, an integrated shunt member insertable into said passage through said opening and arranged in the passage to permit recirculation of the balls between the two threads, said shunt member including two scoops, one for each of said threads and projecting respectively thereinto for redirecting the balls across said shunt, a bridge over which the balls roll in passing between said two threads, and guiding surfaces located adja cent the ends of the bridge for deflecting the balls onto one end and off the other end of said bridge.

6. A non-friction screw and nut assembly com,- prising, in combination, a shaft provided with a threaded portion, a pair of nuts, each provided with threads which are in mating relationship to the threads on the shaft, balls arranged in the mating threads of the shaft and nuts, a nut member arranged concentrically of the shaft and drivably related to the nuts so as to be moved along the shaft in response to shaft rotation, said nut member being provided with two abutments spaced apart axially along said shaft, said nuts being arranged between said abutments and in engaging relationship thereto, and means carried by said nut member for shifting said nuts axially along said shaft to thereby preload the balls.

FARLOW B. BURT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 992,897 Nichols et a1 May 23, 1911 1,239,193 Lindner Sept. 4, 1917 1,509,270 Rodel July 8, 1924 2,441,168 Richardson May 11, 1948 2,455,368 Hoffar Dec. '7, 1948 2,508,261 Hosler May 16, 1950 

